Conventional well drilling, completion or workover techniques comprise the circulation of a fluid injected towards the well bottom through a string of tubes making up the drill string or the production string, the fluid flowing up towards the surface in the annulus defined by the walls of the well and the outside of the string of tubes. During the upflow, a certain amount of fluid enters the porous or fractured geologic formations. This lost amount of fluid is called filtration loss or filtrate. It is generally advisable to limit the amount of filtrate because it represents costly product consumption, requires additional conditioning operations in the mud conditioning plant and also presents risks of destabilization of the well walls or of clogging of the producing or potentially producing geologic zones.
Many filtrate reducing products for water-base fluids, such as drilling fluids, completion fluids or workover fluids, are known in the profession. The use of organic colloids such as starch or CMC (carboxymethylcellulose) may for example be cited. U.S. Pat. No. 4,784,693 mentions the use of a HMHEC polymer or hydrophobically modified hydroxyethylcellulose as a filtrate reducer for a cement slurry with a string of tubes in a well. However, the specific purpose and the composition of a cement slurry, its behavior and its physical or rheological characteristics are different from those of a fluid, for example a drilling, a completion or a workover fluid. In fact, the water content, the composition, the salinity and the solid-liquid ratio of a cement slurry are notably suited for a fluid intended to solidify in the well. On the contrary, a fluid such as a drilling, a completion or a workover fluid is suited for being injected towards the well bottom from a surface pumping plant, then either for flowing up to the surface in order to be processed and/or controlled prior to a possible new injection cycle, or for remaining in the well but while keeping substantially the same physico-chemical characteristics as originally.